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Metformin

Generic Name: metformin (met FOR min)
Brand Names: Fortamet, Glucophage, Glucophage XR, Glumetza. Riomet

Medically reviewed on August 7, 2018

What is metformin?

Metformin is an oral diabetes medicine that helps control blood sugar levels.

Metformin is used together with diet and exercise to improve blood sugar control in adults with type 2 diabetes mellitus.

Metformin is sometimes used together with insulin or other medications, but it is not for treating type 1 diabetes.

Important Information

You should not use metformin if you have severe kidney disease or diabetic ketoacidosis (call your doctor for treatment).

If you need to have any type of x-ray or CT scan using a dye that is injected into your veins, you will need to temporarily stop taking metformin.

You may develop lactic acidosis, a dangerous build-up of lactic acid in your blood. Call your doctor or get emergency medical help if you have unusual muscle pain, trouble breathing, stomach pain, dizziness, feeling cold, or feeling very weak or tired.

Before taking this medicine

You should not use metformin if you are allergic to it, or if you have:

  • severe kidney disease; or

  • metabolic acidosis or diabetic ketoacidosis (call your doctor for treatment).

If you need to have surgery or any type of x-ray or CT scan using a dye that is injected into your veins, you will need to temporarily stop taking metformin. Be sure your caregivers know ahead of time that you are using this medication.

Tell your doctor if you have ever had:

  • kidney disease (your kidney function may need to be checked before you take this medicine);

  • high ketone levels in your blood or urine;

  • heart disease, congestive heart failure;

  • liver disease; or

  • if you also use insulin, or other oral diabetes medications.

You may develop lactic acidosis, a dangerous build-up of lactic acid in your blood. This may be more likely if you have other medical conditions, a severe infection, chronic alcoholism, or if you are 65 or older. Ask your doctor about your risk.

Follow your doctor's instructions about using this medicine if you are pregnant. Blood sugar control is very important during pregnancy, and your dose needs may be different during each trimester of pregnancy. Tell your doctor if you become pregnant while taking metformin.

Metformin may stimulate ovulation in a premenopausal woman and may increase the risk of unintended pregnancy. Talk to your doctor about your risk.

You should not breast-feed while using this medicine.

Metformin should not be given to a child younger than 10 years old. Some forms of metformin are not approved for use by anyone younger than 18 years old.

How should I take metformin?

Take metformin exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Take metformin with a meal, unless your doctor tells you otherwise. Some forms of metformin are taken only once daily with the evening meal. Follow your doctor's instructions.

Do not crush, chew, or break an extended-release tablet. Swallow it whole.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Some tablets are made with a shell that is not absorbed or melted in the body. Part of this shell may appear in your stool. This is normal and will not make the medicine less effective.

Low blood sugar (hypoglycemia) can happen to everyone who has diabetes. Symptoms include headache, hunger, sweating, irritability, dizziness, nausea, fast heart rate, and feeling anxious or shaky. To quickly treat low blood sugar, always keep a fast-acting source of sugar with you such as fruit juice, hard candy, crackers, raisins, or non-diet soda.

Your doctor can prescribe a glucagon emergency injection kit to use in case you have severe hypoglycemia and cannot eat or drink. Be sure your family and close friends know how to give you this injection in an emergency.

Blood sugar levels can be affected by stress, illness, surgery, exercise, alcohol use, or skipping meals. Ask your doctor before changing your dose or medication schedule.

Metformin is only part of a complete treatment program that may also include diet, exercise, weight control, regular blood sugar testing, and special medical care. Follow your doctor's instructions very closely.

Your doctor may have you take extra vitamin B12 while you are taking this medicine. Take only the amount of vitamin B12 that your doctor has prescribed.

Store at room temperature away from moisture, heat, and light.

See also: Dosage Information (in more detail)

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose can cause severe hypoglycemia or lactic acidosis.

What should I avoid while taking metformin?

Avoid drinking alcohol. It lowers blood sugar and may increase your risk of lactic acidosis.

See also: Metformin and alcohol (in more detail)

Metformin side effects

Get emergency medical help if you have signs of an allergic reaction to metformin: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Some people using this medicine develop lactic acidosis, which can be fatal. Get emergency medical help if you have even mild symptoms such as:

  • unusual muscle pain;

  • feeling cold;

  • trouble breathing;

  • feeling dizzy, light-headed, tired, or very weak;

  • stomach pain, vomiting; or

  • slow or irregular heart rate.

Common metformin side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

Metformin dosing information

Usual Adult Dose for Diabetes Type 2:

Immediate-release:
Initial dose: 500 mg orally twice a day or 850 mg orally once a day
Dose titration: Increase in 500 mg weekly increments or 850 mg every 2 weeks as tolerated
Maintenance dose: 2000 mg daily in divided doses
Maximum dose: 2550 mg/day

Extended-release:
Initial dose: 500 to 1000 mg orally once a day
Dose titration: Increase in 500 mg weekly increments as tolerated
Maintenance dose: 2000 mg daily
Maximum dose: 2500 mg daily

Comments:
-Metformin, if not contraindicated, is the preferred initial pharmacologic agent for treatment of type 2 diabetes mellitus.
-Immediate-release: Take in divided doses 2 to 3 times a day with meals; titrate slowly to minimize gastrointestinal side effects. In general, significant responses are not observed with doses less than 1500 mg/day.
-Extended-release: Take with the evening meal; if glycemic control is not achieved with 2000 mg once a day, may consider 1000 mg of extended-release product twice a day; if glycemic control is still not achieve, may switch to immediate-release product.

Use: To improve glycemic control in adults with type 2 diabetes mellitus as an adjunct to diet and exercise.

Usual Pediatric Dose for Diabetes Type 2:

10 years or older:
Immediate-release:
Initial dose: 500 mg orally twice a day
Dose titration: Increase in 500 mg weekly increments as tolerated
Maintenance dose: 2000 mg daily
Maximum dose: 2000 mg daily

Comments: Take in divided doses 2 to 3 times a day with meals. Titrate slowly to minimize gastrointestinal side effects.

Safety and effectiveness of metformin extended-release has not been established in pediatric patients less than 18 years of age.

Use: To improve glycemic control in children with type 2 diabetes mellitus as an adjunct to diet and exercise.

What other drugs will affect metformin?

Many drugs can interact with metformin, making it less effective or increasing your risk of lactic acidosis. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use metformin only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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